That shotgun sure is useless. I wonder how he even managed to make it? Did they actually pay him, a slave, money?
Hopefully the author stops being so obsessed with having the MC make exact replicas of guns and instead allows them to become powerful magic tools. The MC needs to find a way to create usable bullets that store lots of magic in them or something. Heck, if he could find a way to make a tool that stores usable mana then he wouldn't run out so fast when casting spells. If the storage tank is big enough then anyone could reach S class, for a limited time.